Activating Agents for Hafnium-Based Metallocene Components

ABSTRACT

The present invention discloses an active metallocene catalyst system prepared with a hafnium-based metallocene catalyst system and an activating agent comprising an aluminoxane and a sterically hindered Lewis base.

This invention relates to the activation of hafnium-based metallocenecatalyst components.

Polyolefins such as polyethylenes having a high molecular weightgenerally have improved mechanical properties over their low molecularweight counterparts.

It has been observed that hafnium-based metallocene catalyst componentscan be used in catalyst systems that produce homo- and co-polymers ofalpha-olefins having very high molecular weight. They also have anexcellent response to hydrogen. Their activity is however prohibitivelylow.

Until recently the low activity of the hafnium-based metallocenecatalyst systems was believed to be inherent to the metal property.Recently, Rieger et al (Rieger B., Troll C., and Preuschen J., inMacromolecules 2002, 35, 5742-5743) or Preuschen et al. inUS-A-2003/0187158 have shown that the activity of some “dual-site”hafnium-based metallocene catalyst systems may be improved when boratesare used as activating agents and when the solvent is propene. Thesesame catalyst systems, when used with methylaluminoxane (MAO) show avery low activity. It was thus concluded from these studies that MAO isan inefficient activating agent for hafnium-based catalyst systems.

There is thus a need to improve the activity of the metallocene catalystsystems comprising hafnium-based catalyst components.

It is an object of the present invention to improve the activity of themetallocene catalyst systems comprising hafnium-based catalystcomponents.

It is also an aim of the present invention to provide polyolefins havingan improved high molecular weight fraction.

It is a further aim of the present invention to provide the use of ahafnium-based metallocene catalyst component to prepare polyolefins withimproved mechanical properties

-   -   Accordingly, the present invention discloses an active catalyst        system comprising:        -   a hafnium-based catalyst component;        -   an activating agent having a low or no co-ordinating            capability comprising an aluminoxane and a sterically            hindered Lewis base.

When an aluminoxane is used as activating agent, some amount of aluminumalkyl is always simultaneously and inevitably present. Surprisingly, thepresent inventors have identified that this aluminium alkyl isresponsible for the low activity of the hafnium-based metallocenecatalyst systems. It is therefore an object of the present invention toprovide a method to trap the aluminium alkyl by a chemical agent that isnot detrimental to the active cationic species. Such agent is asterically hindered Lewis base.

-   -   The hafnium-based metallocene components of the present        invention have a structure according to formula (I):

R″(CpR_(n))(FluR′_(m))Hf Q₂  (I)

-   -   wherein        -   Cp is a cyclopentadienyl ring;        -   Flu is a fluorenyl ring;        -   each R is the same or different and is hydrogen or a            hydrocarbyl radical such as alkyl, alkenyl, aryl, alkylaryl            or arylalkyl radical containing from 1 to 20 carbon atoms or            two carbon atoms are joined together to form a C4-C6 ring;        -   each R′ is the same or different and is hydrogen or a            hydrocarbyl radical such as alkyl, alkenyl, aryl, alkylaryl            or arylalkyl radical containing from 1 to 20 carbon atoms        -   R″ is a structural bridge between two Cp rings;        -   Q is a hydrocarbyl radical such as aryl, alkyl, alkenyl,            alkylaryl or arylalkyl radical having from 1 to 20 carbon            atoms, a hydrocarboxy radical having from 1 to 20 carbon            atoms or a halogen and can be the same or different from            each other;        -   n is an integer from 0 to 4 and m is an integer from 0 to 8.

By substituted, it is meant that any of the positions on thecyclopentadienyl or on the fluorenyl derivative may comprise asubstituent in place of a hydrogen atom.

The type of bridge present between the ligands in the present catalystcomponent is not particularly limited. Typically R″ comprises analkylidene group having from 1 to 20 carbon atoms, a germanium group(e.g. a dialkyl germanium group), a silicon group (e.g. a dialkylsilicon group), a siloxane group (e.g. a dialkyl siloxane group), analkyl phosphine group or an amine group. Preferably, the substituent onthe bridge comprises a hydrocarbyl radical having at least one carbon,such as a substituted or unsubstituted ethylenyl radical, for example—CH₂—CH₂— (Et). Most preferably R″ is Ph₂C, Et or Me₂Si.

Q is preferably a halogen and most preferably it is Cl.

The substituent or substituents present on the ligands are notparticularly limited. If there is more than one substituent, they can bethe same or different. Typically, they are independently selected from ahydrocarbyl group having from 1 to 20 carbon atoms.

The position of the substituent or substituents on the ligands is notparticularly limited. The ligands may thus have any substitution patternincluding unsubstituted or fully substituted. However, thecyclopentadienyl group is preferably substituted in the 3- and/or5-positions or in the 2- and/or 4-positions. The fluorenyl group ispreferably unsubstituted. If substituted, the substituents arepreferably in the 3- and/or 6-positions or in the 2- and/or 7-positions.In this description, position 1 denotes the position on thecyclopentadienyl group that is attached to the bridge.

The type and position of the substituents is determined by theproperties sought in the resulting polymer. If a syndiotactic polyolefinis desired, the substituents are selected to confer Cs symmetry to thecatalyst component, whereas a C1 or a C2 substitution pattern isselected when isotactic polyolefins are desired.

In another embodiment according to the present invention, the hafniumcatalyst component may be described by the formula II

R″(FluR′_(m))X Hf Q₂  (II)

wherein R″, Cp, R′ and Q have already been defined and wherein X is anhetero atom ligand with one or two lone pair electrons and selected fromthe group 15 or 16. Preferably, X is nitrogen, phosphorus oxygen orsulphur and it can be substituted or unsubstituted.

Preferably the metallocene component is a bridgedcyclopentadienyl-fluorenyl complex, more preferably it has Cs or C1symmetry substitution pattern.

When Cs symmetry is desired, both the cyclopentadienyl and the fluorenylgroups are preferably unsubstituted.

When a C1 symmetry is desired, the preferred substituent on thecyclopentadienyl is a in a position distal to the bridgehead position,most preferably it is a methyl or tert-butyl in position 3. Thefluorenyl is preferably unsubstituted.

The activating agent has low or no coordinating capability and comprisesan aluminoxane and a sterically hindered Lewis base or a compoundcomprising one or more Lewis basic functionalities. Low coordinationcapability means that the compound can bind to the metal but is easilydisplaced by the olefin in the process of polymerisation. The aluminiumalkyl that is inevitably associated with the aluminoxane is an electroncaptor (Lewis acid) and it is neutralised by the addition of an electrondonor. The electron donor must be sufficiently bulky not to interferewith the hafnium.

The aluminoxanes are well known and preferably comprise oligomericlinear and/or cyclic alkyl aluminoxanes represented by the formula:

for oligomeric, linear aluminoxanes and

for oligomeric, cyclic aluminoxane,wherein n is 1-40, preferably 10-20, m is 3-40, preferably 3-20 and R isa C₁-C₈ alkyl group and preferably methyl.

The sterically hindered Lewis base or the compound comprising one ormore Lewis basic functionalities can be selected from compounds offormula

R*_(a-c)E(G-R*_(b-1))_(c)

or of formula

R*(G-R*_(b-1))_(c)

wherein G is a group 15 or 16 element of the periodic Table, b is equalto the coordination number of G, E is a group 14 or 15 element of theperiodic Table, a is the coordination number of E, c is an integer from1 to 4, at most equal to a and each R* is independently a hydrogen or anunsubstituted or substituted hydrocarbyl.

Dimeric, trimeric, tetrameric or oligomeric versions of these compoundsmay also be used.

Suitable compounds that can be used in the present invention areN,N-dimethylaniline, ethylamine, diethylamine, triethylamine,triphenylamine, triphenylphosphine, hexamethylphosphorus triamide,diethylether, ethanol, phenol, thiophenol,2,6-di-t-butyl-4-methylphenol, tetraethoxysilane, phenyltriethoxysilane,diphenyldiethoxysilane, triphenylethoxysilane, diethyldiethoxysilane.

Preferably, the Lewis base added to the aluminoxane in order to trap thealuminium alkyl is a sterically hindered or multi-substituted phenol.

The aluminoxane and Lewis base are mixed together and left to react fora period of time of from 30 minutes to 2 hours, preferably about onehour in order to reach equilibrium.

The amount of aluminoxane added provides a ratio Al/Hf of from 100 to5000, preferably of from 500 to 2000.

The productivity of the catalyst system is critically dependent upon themole ratio R of Lewis base over total aluminium (aluminoxane+aluminiumalkyl). Preferably R ranges from 0.5 to 0.9, more preferably from 0.55to 0.75. If the amount of Lewis base is too large it may act as apoison.

The productivity of the hafnocene-based catalyst system according to thepresent invention is improved by a factor of at least 20.

The invention also provides a method for homo- or co-polymerisingolefins that comprises the steps of:

-   -   A. providing a catalyst system comprising a hafnium-based        catalyst component, an activating agent comprising an        aluminoxane and a sterically hindered Lewis base, and an        optional support;    -   B. introducing the catalyst system in a polymerisation zone        containing an olefin monomer and an optional co-monomer;    -   C. maintaining the reaction zone under polymerisation        conditions;    -   D. extracting the desired polyolefin.

The catalyst system may be employed in a solution polymerisationprocess, which is homogeneous, or a slurry process, which isheterogeneous. In a solution process, typical solvents includehydrocarbons having from 4 to 7 carbon atoms such as heptane, toluene orcyclohexane. In a slurry process it is necessary to immobilise thecatalyst system on an inert support, particularly a porous solid supportsuch as talc, inorganic oxides and resinous support materials such aspolyolefins. Preferably, the support material is an inorganic oxide inits finely divided form.

Suitable inorganic oxide materials that may be employed in accordancewith this invention include group IIA, IIIA, IVA, or IVB metal oxidessuch as silica, alumina and mixtures thereof. Other inorganic oxidesthat may be employed either alone or in combination with the silica, oralumina are for example magnesia, titania or zirconia. Other suitablesupport materials comprise for example finely divided functionalisedpolyolefins such as finely divided polyethylene.

Preferably, the support is a silica support having a specific surfacearea of from 200 to 700 m²/g and a pore volume of from 0.5 to 3 ml/g.

Alternatively, a fluorinated activating support may be used.

The order of addition of the catalyst components and activating agent tothe support material can vary. In accordance with a preferred embodimentof the present invention, the activating agent dissolved in a suitableinert hydrocarbon solvent is added to the support material slurried inthe same or another suitable hydrocarbon liquid and thereafter thecatalyst components are added to the slurry.

Preferred solvents include mineral oils and the various hydrocarbonswhich are liquid at reaction temperature and which do not react with theindividual ingredients. Illustrative examples of the useful solventsinclude the alkanes such as pentane, iso-pentane, hexane, heptane,octane and nonane, cycloalkanes such as cyclopentane, cyclohexane, andaromatics such as benzene, toluene, ethylbenzene and diethylbenzene.

Preferably, the support material is slurried in toluene and the catalystcomponents and activating agent are dissolved in toluene prior toaddition to the support material.

The conditions employed for polymerisation are not particularly limited,provided they are sufficient to effectively polymerise the particularmonomer used as a starting material. Polymerisation may take place inthe presence of hydrogen and of an alkene co-monomer such as 1-butene or1-hexene.

Optionally, pre-polymerisation can be carried out.

Preferably the alpha-olefin is propylene.

LIST OF FIGURES

FIG. 1 represents schemes describing the formation of internal andterminal vinilydene unsaturations in a growing polymer chain.

FIG. 2 represents the ¹H NMR spectra of polypropylene samples preparedwith Me₂C(3-^(t)Bu-Cp)(Flu)MCl₂ wherein M is Zr (2 a) or Hf (2 b)

EXAMPLES Polymerisation of Propylene with PH₂C(Cp)(Flu)MCl₂

Metal M was selected as Zr and Hf respectively. All polymerisationreactions were carried out at a temperature of 50° C. and with a 0.4Msolution of C₃H₆ in toluene. The activating agents were respectivelymethylaluminoxane (MAO) or a mixture MAO/phenol. When MAO was used asactivating agent, the ratio [Al]/[M] was of 1.10³ and when the mixtureMAO/phenol was used as activating agent, the ratio [Al]/[M] was of (1.0to 1.5). 10³ and the ratio [phenol]/[Al] was of 0.6, wherein [Al]represents the total amount of aluminium. The results are displayed inTable I, they include the productivities expressed inkg_(PP)/{[C₃H₆]*mol_(Hf)*h} and polymer properties of active siteenantioselectivity a, fractional abundance of skipped insertions P_(sk)and viscosity-average molecular mass Mv determined in tetralin at 135°C.

TABLE I Activating Productivity * 10⁻³ Metal agent kg_(PP)/{[C₃H₆] *mol_(Hf) * h} σ P_(sk) Mv* Zr MAO 1.1 0.978 0.072 81000 Zr MAO/phenol2.4 0.983 0.054 410000 Hf MAO 0.06 0.948 0.119 16000 Hf MAO/phenol 2.10.941 0.082 610000

It can be seen that the addition of phenol to MAO increases theproductivity of both catalyst systems, but the effect was dramaticallylarger for Hf-based catalyst system than for Zr-based catalyst system.The molecular weight of polypropylene prepared with the hafnium-basedcatalyst system activated with the mixture MAO/phenol was alsoconsiderably larger than that prepared with the zirconium-based catalystsystem, all other polymerisation parameters being the same.

Polymerisation of Propylene with Me₂C(3-R-Cp)(Flu)MCl₂

A first set of polymerisations was carried out with metal M selected ashafnium and with substituent R on the cyclopentadienyl selected asmethyl and tert-butyl respectively. All polymerisation reactions werecarried out at a temperature of 50° C. and with a 0.4 M solution ofpropene in toluene. When MAO was used as activating agent, the ratio[Al]/[M] was of 7.10² and when the mixture MAO/phenol was used asactivating agent the ratio [Al]/[M] was of 6.10² and the ratio[phenol]/[Al] was of 0.6. The results are reported in Table II.

TABLE II Activating Productivity * 10⁻³ Metal agent R kg_(PP)/{[C₃H₆] *mol_(Hf) * h} Hf MAO Me 14 Hf MAO/phenol Me 90 Hf MAO t-Bu — HfMAO/phenol t-Bu 33

Additional polymerisations were carried out with metal M selected ashafnium or zirconium and with substituent R on the cyclopentadienyl ringselected as methyl. The polymerisation temperature and propene partialpressure were selected as indicated in Table III. The polymer propertiesof enantioselectivity at site i, σ_(i) (i=1 or 2), of conditionalprobability P_(ij) of monomer insertion at site j after a previousinsertion at site i (i=1 or 2 and j=1 or 2) are also displayed in TableIII. In all polymerisation reactions, the catalyst system was activatedwith a mixture MAO/phenol having a ratio [phenol]/[Al] of 0.6.

TABLE III Pressure Temp. C₃H₆ Metal ° C. bars σ₁ P₁₂ σ₂ P₂₁ Zr 25 1 0.980.9 0.44 1 Zr 25 8 0.99 0.97 0.44 1 Hf 25 1 0.95 0.82 0.5 1 Hf 25 8 0.950.98 0.52 1 Zr 50 1 0.97 0.66 0.43 1 Zr 50 8 0.98 0.9 0.45 1 Hf 50 10.91 0.66 0.56 1 Hf 50 4 0.956 0.82 0.51 1

At a polymerisation temperature of 25° C., the polymers obtained all hada hemiisotactic-like structure and they all exhibited a weak tendency ofthe growing chain to back skip to the less hindered coordination siteupon diluting the monomer. The enantioselectivity of the more opencoordination site was lower for the hafnocene (95%) than for thezirconocene (98%) and it was not sensitive to monomer concentration.

At a polymerisation temperature of 50° C., the enantioselectivity of themore open coordination site decreased with decreasing monomerconcentration for the hafnocene, whereas it remained unaltered for thezirconocene.

Without wishing to be bound by a theory, this behaviour might be theresult of growing chain epimerisation.

The present inventors have reported in European patent applicationEP-03102060 that the catalyst systems based on catalyst componentMe₂C(3-^(t)Bu-Cp)(Flu)ZrCl₂ generated polypropylene with anunprecedently high level of internal chain unsaturations. These internalchain unsaturations were attributed to β-H elimination followed byallylic chain activation as summarised in FIG. 1.

The hafnocenes of the present invention did not exhibit the tendency toproduce internal unsaturations. Their NMR spectrum indicated on thecontrary a majority of terminal unsaturations. The ¹H NMR spectra in theolefinic region of 400 MHz were recorded for the polymer samplesprepared in toluene with Me₂C(3-^(t)Bu-Cp)(Flu)MCl₂ wherein M is Zr orHf. They are represented in FIGS. 2 a and 2 b respectively. It can beseen from these spectra that the samples prepared with the zirconocene(2 a) have truly internal vinylidene unsaturations, whereas thoseprepared with the hafnocene (2 b) show the two peaks characteristic ofterminal vinylidene unsaturations and additionally a complex pattern at5.0-5.1 ppm that could represent a terminal vinyl.

1-13. (canceled)
 14. A method comprising: preparing a metallocenecatalyst system by combining a hafnium-based metallocene catalystcomponent and an activating agent; wherein the hafnium-based metallocenecatalyst component is of formula IIR″(FluR′_(m))X Hf Q₂  (II) wherein Flu is a fluorenyl ring; wherein eachR′ is the same or different and is hydrogen or a hydrocarbyl radicalcontaining from 1 to 20 carbon atoms; wherein m is an integer from 0 to8; wherein each Q is a hydrocarbyl radical having from 1 to 20 carbonatoms, a hydrocarboxy radical having from 1 to 20 carbon atoms or ahalogen and can be the same or different from each other; wherein X is ahetero atom ligand with one or two lone pair electrons and is selectedfrom group 16; and wherein R″ is a structural bridge between Flu and X;wherein the activating agent has a low or no co-ordinating capabilityand comprises an aluminoxane and a Lewis base, and wherein theactivating agent comprises a ratio of Lewis base to total aluminum offrom 0.5:1 to 0.9:1.
 15. The method of claim 14, further comprising,prior to the combining of the hafnium-based metallocene catalystcomponent and the activating agent, forming the activating agent by:mixing the aluminoxane with the Lewis base; and reacting the aluminoxaneand the Lewis base for a period of time sufficient to reach equilibrium,wherein aluminum alkyl present in the activating agent is neutralized bythe Lewis base.
 16. The method of claim 15, wherein the period of timesufficient to reach equilibrium ranges from 30 minutes to 2 hours. 17.The method of claim 14, wherein the activating agent comprises a ratioof Lewis base to total aluminum of from 0.55:1 to 0.75:1.
 18. The methodof claim 14, wherein the Lewis base is a compound of formula R*_(a-c) E(G-R*_(b-1))_(c) or of formula R*(G-R*_(b-1))_(c) wherein G is a group15 or 16 element of the Periodic Table, b is equal to the valency of G,E is a group 14 or 15 element of the Periodic Table, a is thecoordination number of E, c is an integer from 1 to 4, at most equal toa and each R* is independently a hydrogen or an unsubstituted orsubstituted hydrocarbyl.
 19. The method of claim 14, wherein the Lewisbase is N,N-dimethylaniline, ethylamine; diethylamine; trimethylamine;triphenylamine; triphenylphosphine; hexamethylphosphorus triamide;diethylether; ethanol; phenol; thiophenol,2,6-di-t-butyl-4-methylphenol; tetraethoxysilane; phenyltriethoxysilane;diphenyidiethoxysilane; triphenylethoxysilane; or diethyldiethoxysilane.20. The method of claim 14, wherein the Lewis base is a phenol.
 21. Themethod of claim 20, wherein the phenol is a sterically hindered phenol.22. The method of claim 20, wherein the phenol is a multi-substitutedphenol.
 23. The method of claim 14, wherein the hafnium-basedmetallocene catalyst component and the activating agent are combinedwith a support material.
 24. The method of claim 23, wherein theactivating agent is contacted with the support material prior to thehafnium-based metallocene catalyst component.
 25. The method of claim23, wherein combining the hafnium-based metallocene catalyst componentand the activating agent with the support material comprises: providingthe activating agent dissolved in an inert hydrocarbon solvent;providing the support material slurried in the same inert hydrocarbonsolvent as the activating agent or in another inert hydrocarbon solvent;adding the activating agent to the support material; after adding theactivating agent to the support material, adding the hafnium-basedmetallocene catalyst component to the activating agent and the supportmaterial.
 26. The method of claim 14, wherein R″ is an alkylidene grouphaving from 1 to 20 carbon atoms, a germanium group, a silicon group, asiloxane group, an alkyl phosphine group, or an amine group.
 27. Themethod of claim 14, wherein R″ is a hydrocarbyl radical having at leastone carbon.
 28. The method of claim 14, wherein R″ is CH₂—CH₂, Ph₂C, orMe₂Si.
 29. The method of claim 14, wherein Q is a halogen.
 30. Themethod of claim 29, wherein Q is Cl.
 31. The method of claim 14, whereinX is oxygen or sulphur.
 32. The method of claim 14, wherein thehafnium-based metallocene catalyst component is a bridgedcyclopentadienyl-fluorenyl complex that has a Cs or Cl symmetry.
 33. Themethod of claim 14, wherein the metallocene catalyst system has a ratioAl/Hf of from 100 to
 5000. 34. The method of claim 14, wherein themetallocene catalyst system has a ratio Al/Hf of from 500 to
 2000. 35. Amethod comprising: mixing an aluminoxane containing aluminum alkyl witha Lewis base, wherein the phenol is a multi-substituted phenol; reactingthe aluminoxane and the Lewis base for a period of time sufficient toreach equilibrium, wherein the aluminum alkyl is neutralized by theLewis base, to obtain an activating agent comprising the aluminoxane andthe Lewis base; combining a hafnium-based metallocene catalyst componentand the activating agent; wherein the hafnium-based metallocene catalystcomponent is of formula IIR″(FluR′_(m))X Hf Q₂  (II) wherein Flu is a fluorenyl ring; wherein eachR′ is the same or different and is hydrogen or a hydrocarbyl radicalcontaining from 1 to 20 carbon atoms; wherein m is an integer from 0 to8; wherein each Q is a hydrocarbyl radical having from 1 to 20 carbonatoms, a hydrocarboxy radical having from 1 to 20 carbon atoms or ahalogen and can be the same or different from each other; wherein X is ahetero atom ligand with one or two lone pair electrons and is selectedfrom group 16; and wherein R″ is a structural bridge between Flu and X;wherein the activating agent has a low or no co-ordinating capability,and wherein the activating agent comprises a ratio of Lewis base tototal aluminum of from 0.55:1 to 0.75:1.